Inertial microfluidics for sheath-less high-throughput flow cytometry.

Flow cytometer is a powerful single cell analysis tool that allows multi-parametric study of suspended cells. Most commercial flow cytometers available today are bulky, expensive instruments requiring high maintenance costs and specially trained personnel for operation. Hence, there is a need to develop a low cost, portable alternative that will aid in making this powerful research tool more accessible. In this paper we describe a sheath-less, on-chip flow cytometry system based on the principle of Dean coupled inertial microfluidics. The design takes advantage of the Dean drag and inertial lift forces acting on particles flowing through a spiral microchannel to focus them in 3-D at a single position across the microchannel cross-section. Unlike the previously reported micro-flow cytometers, the developed system relies entirely on the microchannel geometry for particle focusing, eliminating the need for complex microchannel designs and additional microfluidic plumbing associated with sheath-based techniques. In this work, a 10-loop spiral microchannel 100 microm wide and 50 microm high was used to focus 6 microm particles in 3-D. The focused particle stream was detected with a laser induced fluorescence (LIF) setup. The microfluidic system was shown to have a high throughput of 2,100 particles/sec. Finally, the viability of the developed technique for cell counting was demonstrated using SH-SY5Y neuroblastoma cells. The passive focusing principle and the planar nature of the described design will permit easy integration with existing lab-on-a-chip (LOC) systems.

Inertial microfluidics for continuous particle separation in spiral microchannels.

In this work we report on a simple inertial microfluidic device that achieves continuous multi-particle separation using the principle of Dean-coupled inertial migration in spiral microchannels. The dominant inertial forces coupled with the Dean rotational force due to the curvilinear microchannel geometry cause particles to occupy a single equilibrium position near the inner microchannel wall. The position at which particles equilibrate is dependent on the ratio of the inertial lift to Dean drag forces. Using this concept, we demonstrate, for the first time, a spiral lab-on-a-chip (LOC) for size-dependent focusing of particles at distinct equilibrium positions across the microchannel cross-section from a multi-particle mixture. The individual particle streams can be collected with an appropriately designed outlet system. To demonstrate this principle, a 5-loop Archimedean spiral microchannel with a fixed width of 500 microm and a height of 130 microm was used to simultaneously and continuously separate 10 microm, 15 microm, and 20 microm polystyrene particles. The device exhibited 90% separation efficiency. The versatility of the device was demonstrated by separating neuroblastoma and glioma cells with 80% efficiency and high relative viability (>90%). The achieved throughput of approximately 1 million cells/min is substantially higher than the sorting rates reported by other microscale sorting methods and is comparable to the rates obtained with commercial macroscale flow cytometry techniques. The simple planar structure and high throughput offered by this passive microfluidic approach make it attractive for LOC devices in biomedical and environmental applications.

Continuous particle separation in spiral microchannels using Dean flows and differential migration.

Microparticle separation and concentration based on size has become indispensable in many biomedical and environmental applications. In this paper we describe a passive microfluidic device with spiral microchannel geometry for complete separation of particles. The design takes advantage of the inertial lift and viscous drag forces acting on particles of various sizes to achieve differential migration, and hence separation, of microparticles. The dominant inertial forces and the Dean rotation force due to the spiral microchannel geometry cause the larger particles to occupy a single equilibrium position near the inner microchannel wall. The smaller particles migrate to the outer half of the channel under the influence of Dean forces resulting in the formation of two distinct particle streams which are collected in two separate outputs. This is the first demonstration that takes advantage of the dual role of Dean forces for focusing larger particles in a single equilibrium position and transposing the smaller particles from the inner half to the outer half of the microchannel cross-section. The 5-loop spiral microchannel 100 microm wide and 50 microm high was used to successfully demonstrate a complete separation of 7.32 microm and 1.9 microm particles at Dean number De = 0.47. Analytical analysis supporting the experiments and models is also presented. The simple planar structure of the separator offers simple fabrication and makes it ideal for integration with on-chip microfluidic systems, such as micro total analysis systems (muTAS) or lab-on-a-chip (LOC) for continuous filtration and separation applications.